Typical elevator systems include a car and a counterweight confined to travel along guiderails in a vertically extending elevator shaft. The car and the counterweight are connected to each other by hoist ropes. The hoist ropes are wrapped around a sheave located in a machine room at the top (or bottom) of the elevator shaft. In conventional elevator systems, the sheave is powered by an electrical motor. In other elevator systems, the sheave is unpowered, and the drive means is a linear motor mounted on the counterweight.
Rope sway refers to oscillation of the hoist and/or compensation ropes in the elevator shaft. The oscillation can be a significant problem in a roped elevator system. The oscillation can be caused, for example, by vibration emanating from wind induced building deflection and/or the vibration of the ropes during operation of the elevator system. If the frequency of the vibrations approaches or enters a natural harmonic of the ropes, then the oscillation displacements can increase far greater than the displacements. In such situations, the ropes can tangle with other equipment in the elevator shaft, or as the elevator travels, come out of the grooves of the sheaves. If the elevator system use multiple ropes and the ropes oscillate out of phase with one another, then the ropes can become tangled with each other and the elevator system may be damaged.
Several conventional solutions use mechanical devices connected to the ropes to estimate the displacement of the ropes. For example, one solution uses a device attached to a compensating rope sheave assembly in an elevator system to detect rope sway exceeding a certain magnitude. However, a mechanical device attached to a compensating rope is difficult to install and maintain.
Another method uses displacement and the natural frequency of the building for estimating and computing the amount of sway of the rope. This method is general and may not provide precise estimation of the rope sway.
Accordingly, there is a need to improve an estimation of a rope sway suitable for the estimation of the rope sway in real time.